Minimum internal surface temperature Properties of constructions Minimum internal surface temperature

Min. internal surf. temperature It is used for evaluation of the risk of vapor condensation on internal surface and of the risk of mould growth. When does surface condensation occur? Surface temperature is lower than dew point temperature of ambient air.

Definitions Dew point temperature [˚C] humidity of air is 100 %). Temperature with the maximum saturation of air by water vapor (relative humidity of air is 100 %). It depends on temperature and relative humidity of air. E.g. for air with temperature 20 ˚C and rel. humidity 50%, dew point temperature is 9,3 ˚C. If we cool the air with temperature 20 ˚C and rel. humidity 50% to 9,3 ˚C, it will be saturated by water vapor.

Surface humidity above 80% and… Min. internal surf. temperature It is used for evaluation of the risk of vapor condensation on internal surface and of the risk of mould growth. When does mould growth start? - oxygen air RH optimally over 60% temperature opt. 18-28 C nutrients: dust, organic scraps, C+N from air, trace nutrients (rain, breath, fingerprints…) Surface humidity above 80% and…

Min. internal surf. temperature It is used for evaluation of the risk of vapor condensation on internal surface and of the risk of mould growth. Internal surface condensation has no connection with vapor transfer through constructions! (it cannot be influenced by vapor barrier etc.) It depends only on thermal-insulating properties of constructions (R, U, details…) and on boundary conditions.

Min. internal surf. temperature Surface vapor condensation could be eliminated by: 1) increase of surface temperature of construction Possibilities: - improvement of thermal insulation (larger thickness, continuity of insulation in details, thermal breaks…) - warming of construction’s internal surface 2) decrease of dew point temperature of internal air Possibilities: - decrease of internal air humidity (dehumidification, ventilation, limitation of sources)

Temperature factor at internal surface Properties of constructions Temperature factor at internal surface

Temperature factor at internal surface Alternative expression of internal surface temperature – independent on boundary conditions – it is parameter of construction or detail. Internal surface temperature calc. START variable for various boundary conditions Temperature factor at int. surface STOP constant, parameter of construction It is used in catalogues of details… … and for evaluation of requirement (from 2007).

Calculation: Temperature factor at internal surface design temperature of external air in winter period design temperature of internal air (or generally: the same temperature which was used to calculate internal surface temperature θsi )

Calculation: Temperature factor at internal surface surface temperatures calculation: opaque constr.: 0,25 m2K/W windows, doors: 0,13 m2K/W behind furniture: 0,50 m2K/W min. internal surface temperature details: numerical solution necessary, no formulas for direct calculation planar constructions:

Calculation: Temperature factor at internal surface surface temperatures calculation: opaque constr.: 0,25 m2K/W windows, doors: 0,13 m2K/W behind furniture: 0,50 m2K/W min. internal surface temperature details: numerical solution necessary, no formulas for direct calculation Int. surface temperature and temperature factor: problem of critical details, (temp. factor is satisfactory for every planar construction with satisfactory U-value), it is necessary to solve th. bridges planar constructions:

Requirement of ČSN 730540-2: Temperature factor at internal surface dependent on type of construction: windows + doors – elimination of surface condensation other – elimination of mould growth derived from max. acceptable surface RH: 100 % 80 % for interiors with RH  60 %:

and φi=50% (for -5 C in exterior): Temperature factor at internal surface Requirement of ČSN 730540-2: dependent on type of construction: windows + doors – elimination of surface condensation other – elimination of mould growth derived from max. acceptable surface RH: Typical values for θe=-15 C, θai=20,6 C and φi=50% (for -5 C in exterior): windows: fRsi,cr = 0,653 other: fRsi,cr = 0,747 100 % 80 % for interiors with RH  60 %:

for ventilated constructions: Temperature factor at internal surface Requirement of ČSN 730540-2: for interiors with RH > 60 %: requirement does not have to be fulfilled but following must be ensured: satisfactory thermal transmittance excellent function during surface condensation adjacent constructions without defects from moisture elimination of mould growth in some other way than high surface temperature RH near surface can be also decreased using AC for ventilated constructions: temp. factor at internal surface of external deck: variable in direction of air flow usually evaluated only at outlet

Thermal bridges and joints: calculations and design recommendation Properties of constructions Thermal bridges and joints: calculations and design recommendation

parts of constructions between constructions Thermal bridges and joints Terminology: Thermal bridges and joints: parts of construction with increased heat flow caused by more conductive materials or geometry parts of constructions between constructions Types of bridges and joints: geometrical (due to shape) constructional (due to load bearing structure) systematic (regularly repeating) convective (due to convection through leakages)

The most common appearance Thermal bridges: slope roofs with insulation timber buildings curtain walling sandwich panels anchors, fasteners etc. etc. Thermal joints: all connections wall-window connection wall-roof, wall-ceiling and wall-floor on ground cantilevers (balconies, overhangs) any local disruption of thermal insulation etc. etc.

Thermal bridges and joints Governing equations: part. diff. equation for heat conduction 3D steady state conduction in general, numerical solution necessary (FEM, FDM) 2D steady state conduction

Thermal bridges and joints Numerical solutions: using software (e.g. COMSOL, ANSYS, FLIXO,AREA…) specific steps are dependent on SW generally: identification of th. bridge model selection (2D, 3D) simplification specification of materials and conditions model creation calculation interpretation and evaluation of results quality of model depends on purpose: windows x common details correct Rsi necessary (0,25 a 0,13)! specified for surfaces in contact with air sections = adiabatic boundaries (without heat flow over boundary) condition in ground (mean annual temperature, usually 5 C) in 3 m (1 m) under the floor

Thermal bridges and joints Numerical solutions: using software (e.g. COMSOL, ANSYS, AREA, CUBE3D) specific steps are dependent on SW generally: identification of th. bridge model selection (2D, 3D) simplification specification of materials and conditions model creation calculation interpretation and evaluation of results quality of model depends on purpose: windows x common details procedures in EN ISO 10211, EN ISO 10077 and EN ISO 13947 It is necessary to include also a part of construction around th. bridge, boundary = min. 1 m or 3 * bridge thickness or symmetry axis.

Thermal bridges and joints Example of calculation: input information calculation results geometry of the model fRsi = 0,881

Thermal bridges and joints What are the effects of thermal bridge? decreased internal surface temperature increased external surface temperature increased heat flow visually: higher density of isotherms

Elimination of bridges and joints Possibilities: basic rule: decrease the number of thermal bridges and joints (mainly of balconies, overhangs, cantilevers…) if not possible, try to change static scheme (use separate columns instead of cantilever etc.) always continuous insulation! „iso – beam“

…preferably from external side Elimination of bridges and joints Possibilities: basic rule: decrease the number of thermal bridges and joints (mainly of balconies, overhangs, cantilevers…) if not possible, try to change static scheme (use separate columns instead of cantilever etc.) always continuous insulation! …preferably from external side and in max. thickness!

Elimination of bridges and joints Possibilities: - simple shapes are better think about real possibilities of building process! the simpliest shapes with smallest problems

Elimination of bridges and joints Possibilities: - decrease the area of external surfaces (beware of high roof parapets!) - optimalisation of the shape Extremely disadvantageous: large external surface smal internal surface Spittelau Viadukt Zaha Hadid, Vídeň

Elimination of bridges and joints use up-to-date technologies insulation fasteners (basalt) in sandwich walls insulation pads under anchors insulatiuon of wall footing (here Wienerberger) hardened plastics: Purenit, Compacfoam

Elimination of bridges and joints eliminate even „small“ thermal bridges hidden screw EPS plug injection anchors Spiral Anksys up to 300 mm

Elimination of bridges and joints eliminate even „small“ thermal bridges Importance of thermal bridges and joints rises. The better the primary construction, the worse problem the bridge is. Heat loss through thermal joints: formerly units of % today even tens of % from the building total heat loss. Fixing blocks Dosteba – various types, even for high load